1. Field of Invention
The present invention relates to a variable resistance device adapted to be incorporated in an exercise machine to provide a selectively-variable degree of resistance for the exercise machine.
2. Description of Prior Art
An exercise machine, by definition, needs to provide the user with a degree of resistance for muscular exercise. In almost all forms of exercise, there is a requirement in exercise machines for the degree of resistance to be varied.
First, there is the need for the user to vary the degree of resistance with a minimum of effort and complexity.
Second, another need is for the selected degree of resistance to be precise and repeatable. This is particularly so for resistance machines used by athletes who require a precise calibration of resistance values so that the values can act as a precise reference point for monitoring their exercise routines. As an example, sporting institutions would benefit from a precisely calibrated exercise machine for testing large numbers of athletes over a long period of years, so that there can be confidence that the degree of resistance used in a set of test exercises can be guaranteed to remain constant over the period of years. This degree of repeatability is often difficult to maintain, for instance, in exercise machines that use magnetic resistance, and wind resistance. In the case of magnetic resistance, the calibration of the magnets can alter over time. Wind resistance can be affected by the amount of atmospheric pressure, particularly when the same machine is used at different altitude levels.
There is also the need for the user to selectively change the degree of resistance, even within a workout. In PCT/US88/01580, International Publication WO88/08735 (Duke), an exercise machine, which simulates rowing, is provided with a resistance device which consists of a paddle that rotates in a cylindrical water-filled container. The degree of fluid in the container determines the degree of resistance experienced by the user. This prior art machine is provided with a handle connected to a drive cord. The user pulls and releases the drive cord, thereby simulating the stroke an oar when rowing a boat. However, in this prior art device, resistance is varied by a cumbersome method of wrapping a greater or lesser quantity of strap around the drive spool. It is believed that this increases or decreases the tangential forces as the circumference is increased or decreased.
Moreover, this manner of varying the resistance does not readily provide an accurate repeatable degree of resistance, since the user might not know how much cord has been wrapped, nor how much cord remains unwrapped. Also, the range of resistance-afforded by wrapping and unwrapping a cord-is narrow in range, so that the user does not have the benefit of using a wide range of resistance values.
In the prior art, which relate to resistance in the form of paddles that rotate in baths of water, there are systems which involve a first and second chamber, wherein liquid is transferred between the chambers so as to vary the amount of liquid in the primary container in which the paddle rotates, for example U.S. Pat. No. 5,944,637 (Stickler), and U.S. Pat. No. 5,195,936 (Mao). In these prior art, however, the liquid is forced from a first chamber into a second chamber through the same aperture or apertures. In other words, there is a two-way flow of liquid through the same aperture. Thus, these prior art apparatus must be provided with complex mechanisms needed to force the liquid through the same aperture, initially, in a first direction, then back through the same aperture in a second direction. The need for applying such forces means that the exercise machines require complex and thus more expensive mechanisms to force the liquid in and out of the apertures which link the chambers.
An objective of the present invention is to overcome or at least ameliorate one or more of the above problems in the prior art, or to provide an improved alternative.